IGZO (Indium Gallium Zinc Oxide) semiconductors have attracted broad attention because of their advantages such as high electron mobility, low leakage current, and low temperature required for preparation. For a traditional top-gate self-aligned structure, after an active layer, a gate electrode layer, and a gate insulator layer are patterned, plasmas (Ar, He, N2, etc.) are used to make S/D (source/drain) contact regions conductive so as to reduce impedance. However, in a subsequent annealing process, impedance in the regions may recover gradually, which affects the carrier transport. As a result, electric properties of a thin-film transistor are affected.